A box-shaped aquarium has horizontal dimensions 0.5 m by 1 m, and depth 0.5 m, and is filled two-thirds of the way to the surface. As it is being transported downwards in an elevator, someone accidentally presses the emergency stop button, such that the elevator comes to rest with a deceleration of magnitude 2g, where the gravitational acceleration g = 9.81 m/s2 . Calculate the pressure difference between the bottom and the surface of the tank.